During MHC class II antigen presentation, HLA-DM catalyzes the exchange of CLIP for antigenic peptide in the MHC class II compartment. Which molecule initially occupies the peptide-binding groove of MHC class II molecules to prevent premature peptide binding in the endoplasmic reticulum?
- A Invariant chain (Ii, CD74) ✓
- B TAP transporter
- C Calnexin
- D HLA-DO
Correct answer: A. Invariant chain (Ii, CD74)
Explanation
The invariant chain (CD74) binds to MHC class II molecules in the endoplasmic reticulum, blocking the peptide-binding groove until the MHC II reaches the endosomal compartment. C fragment of the invariant chain called CLIP remains in the groove until HLA-DM facilitates its exchange for antigenic peptide. TAP transports peptides for MHC class I. HLA-DO modulates HLA-DM activity but does not occupy the groove initially.
Reference: Janeway's Immunobiology, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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